The present invention relates to an apparatus for freeing blood of metabolic products and, more especially relates to dialysis with a single connection with the patient's circulatory system, that is to say a single needle dialysis, using a first pipe running away from this connection and a second pipe running towards it, a dialysis diaphragm joined up with these pipes, at least one pump and at least one part with a valve function in at least one of the pipes for controlling the input and output of blood in the circuit outside the patient's body, a blood accumulator forming part of one of the pipes, and an automatic controller for the pump and the part functioning as a valve.
Unlike normal hemodialysis in which the patient's skin and vessels have to be punctured with separate needles for taking the blood from his or her body and running it back thereinto, single needle dialysis makes do with one needle, such dialysis offering the useful effect that the number of punctures is decreased to one half so that, on the one hand, there is less damage to the vessels while on the other hand pain produced on puncturing the skin is cut down. In particular in the case of acute dialysis a single opening into a vessel is all that is needed so that, in cases of emergency, treatment is made much simpler.
However, the shortcoming caused by single needle dialysis is the stop-go turning on and off of the inflow and outflow of blood and the fact that, in part, cleaned blood and uncleaned blood are mixed together at the needle used for joining up the patient with the dialysis apparatus in single needle dialysis.
Unlike continuous dialysis using two needles, in which the pressure within the dialysis system may undergo, generally speaking, adjustment within more or less tight limits, in single needle dialysis an increase and decrease in pressure takes place all the time because of the fact that at any one time blood is being taken up by the apparatus and then later is run off back into the body. For this reason, it is hard to keep to the desired flow rates at a given average pressure in a single needle operation so that attempts have been made at taking care of such shortcomings.
In fact, German Offenlegungsschrift specification No. 2,417,900 relates to a blood dialysis apparatus in which immediately downstream from an y-like needle, whose ends are joined with the arterial and vein pipes, there is a pump, a dialysis diaphragm, and a bubble trap in the vein pipe. In one embodiment, using a further pipe the bubble trap is joined up with a pressure monitor controlling a double clip unit, placed right on the y-like end of the needle, for clipping and shutting off, in one case, the arterial pipe and, in the other case, the vein pipe. In this system there is a pressure-dependent control in a bubble trap with rigid walls, the blood pumped into the trap in fact elastically compressing the air space thereover and, for this reason, activating the pressure monitor which, for its part, is used for controlling the double pipe clip unit.
Such a system has a shortcoming inasfar as the pressure limit monitors or gases, necessary for pressure control, are high in price and likely to get out of order, while on the other hand pressure changes at the dialysis diaphragm have an undesired effect on the flow of liquid through the diaphragm so that a balanced liquid take-up by the dialyzer is made harder or may be stopped completely. Furthermore, with such a pressure control system there will be the danger of aspiration in a backward direction of liquid, which may be possibly contaminated, and of air because the pipe system is not completely air-tight.
German Offenlegungsschrift specification No. 2,636,290 is directed to an apparatus for controlling and monitoring blood flow in dialysis in which, in place of the bubble trap as noted, there is a measuring space with, once again, stiff side walls with sensors within them for the purpose of controlling the volume of blood within such measuring space so as to keep to a value somewhere between upper and lower limiting values. At its top end, this measuring space has a unit for evening out pressure, as for example a sterile filter, a bag or a bladder so that, generally speaking, the complete measuring space is freed of pressure. Because of this pressureless condition, this known system has to have two pumps, that is to say one for the input and the other for the output of blood upstream and downstream from the dialysis diaphragm. The use of hose clips, which would be very much cheaper than using a pump, is not possible for this reason, so that the price of making such a dialysis apparatus is very much higher. A further factor going into the price of the apparatus is that vacuum has to be provided at the dialysis diaphragm itself on its dialysate side by a special unit for taking the liquid from the patient at the desired rate.
Such shortcomings could be avoided by a suggestion which has been made in the British Medical Journal, Vol. 281 (1980), page 1109. This paper suggests the use of a single needle dialysis system in which there is a blood input pump in the arterial pipe, running towards the dialysis diaphragm, a flexible accumulator and a blood output pump, there only being one pipe clip on the vein pipe for shutting and opening the pipe. In the operation of the system, in the first place, the accumulator is first pumped full by the one pump without any building up of pressure therein. After turning off this pump, the other pump is turned on and, at the same time, the pipe clip on the vein pipe is opened. The blood in the accumulator is pumped back past the dialysis diaphragm through the vein pipe to the patient, pressure changes in this system being kept down to less than 10 mm Hg. Because no pressure is produced on filling up the accumulator, a second pump is necessarily needed for pumping the blood through the dialysis system. Furthermore, the transdiaphragm pressure adjustment at the dialysis diaphragm has to be controlled from the outside, thus greatly increasing the price of the apparatus and making its operation complex.